GAZA—A high-level attempt by the UN chief and the U.S. secretary of state to end deadly Israel-Hamas fighting was off to a rough start Monday.

Israeli tanks, meanwhile, shelled a hospital in central Gaza, killing four people and wounding dozens as the daily death toll surpassed 100 for a second day. Israel said the shelling targeted rockets hidden near the compound, and accused militants of using civilians as shields.

On the Israeli side, seven more soldiers were killed in clashes with Gaza fighters Monday, bringing the military death toll to 25 — more than twice as many as in Israel’s last Gaza ground war in 2009.

The mounting bloodshed brought UN Secretary-General Ban Ki-moon and U.S. Secretary of State John Kerry to Cairo on Monday for a new ceasefire push. However, the gaps remain wide and no credible mediator has emerged.

Gaza’s Hamas rulers signalled they won’t agree to an unconditional ceasefire, Israel’s prime minister said he’ll do whatever is necessary to keep Israelis safe from Hamas attacks and the overall Palestinian death toll surpassed 560.

Across Gaza, Israeli fighter planes hit homes and a highrise building, burying families in the rubble. The strike on the Gaza City tower brought down most of the building, killing 11 people — including six members of the same family — and wounding 40, said Palestinian health official Ashraf al-Kidra.

At least 565 Palestinians have been killed and more than 3,600 wounded in the past two weeks, al-Kidra said.

Two civilians have also died in Palestinian rocket attacks on Israeli cities and scores of soldiers have been injured.

The U.S. State Department says U.S. citizens Nissim Sean Carmeli and Max Steinberg were among the Israeli soldiers who died in Gaza Sunday.

Egypt, Israel and the U.S. back an unconditional ceasefire, to be followed by talks on a possible new border arrangement for Gaza. Israel and Egypt have severely restricted movement in and out of Gaza since Hamas seized the territory in 2007.

Hamas, with some support from Qatar and Turkey, wants guarantees on lifting the blockade before halting fire. The Islamic militant group has no faith in mediation by Egypt’s rulers, who deposed a Hamas-friendly government in Cairo a year ago and tightened restrictions on Gaza — to the point of driving Hamas into its worst financial crisis since its founding in 1987.

The top Hamas leader in Gaza, Ismail Haniyeh, said Monday that Gaza’s 1.7 million people share Hamas’ goal of forcing Israel and Egypt to lift the blockade.

“We cannot go back, we cannot go back to the silent death (of the blockade),” he said. “Gaza has decided to end the blockade by its blood and by its courage.”

After a meeting with Egyptian Foreign Minister Sameh Shukri, Ban said “violence must stop by all sides,” and that they must enter negotiations, seemingly siding with Cairo’s approach.

However, Ban also said: “We can’t claim victory simply by returning matters to where they stood before they led to terrible bloodshed.”

The border blockade has set Gaza back years, wiping out tens of thousands of jobs through bans on most exports and on imports of vital construction materials Israel says could be diverted by Hamas for military use. Israel allows many consumer goods into Gaza, but experts say Gaza’s economy cannot recover without resumed exports.

Israeli Prime Minister Benjamin Netanyahu told Sky News Arabia that the goal of Israel’s strikes on Gaza is “to restore quiet and security for the people of Israel for a significant period of time.”

“We’ll take whatever action is necessary to achieve that goal,” he said, adding that Israel has accepted ceasefire offers while Hamas has rejected them.

Israel has claimed it is trying to minimize civilian deaths and accused Hamas of using civilians as human shields.

However, Israeli strikes on homes have driven up casualties. About half of the dead were killed in their homes, according to the Al Mezan Centre for Human Rights. Various Palestinian rights groups estimated at least 425 homes across Gaza have been attacked by the military since July 8. Israel has only said it is hitting Hamas rocket launchers and command and control centres.

Three Israeli soldiers were killed in clashes in Gaza, while a female suicide bomber was shot before she could detonate her explosive belt among soldiers, the military said. Another four Israeli soldiers were killed in a firefight when Hamas militants sneaked into Israel through a tunnel from Gaza.

Since Israel’s ground operation in Gaza began last week, Israeli soldiers have uncovered 45 shafts leading into about 16 underground tunnels, some as deep as 30 metres.

Israel says the tunnels, some starting from homes and mosques, are a strategic threat because they reach inside Israel.